1. Field of the Invention
The present invention relates to an apparatus for manufacturing a photogravure plate for a gravure.
2. Description of the Background Art
During a step of manufacturing a plate for a gravure, an engraving head creates a number of recess portions (cells) which express a gradation on a cylinder, i.e., a plate material, based on gravure data which are monochrome gradation image data. If power failure occurs during this step of manufacturing a plate, an engraving operation for creating cells on the cylinder is stopped. Although the engraving operation may be resumed from the interruption point when power is recovered (hereinafter referred to as "recovery of power"), since a start-up characteristic of the engraving head does not always remain exactly the same, the quality of a plate is deteriorated. In other words, since an operation of the engraving head in the gravure is characterized in that the depth of a cell becomes shallower than a depth which corresponds to gravure data at the starting point and the end point of engraving, once engraving is interrupted because of power failure, engraving after resumed creates cells which are shallower than depths which correspond to the gravure data, and therefore, it is impossible to obtain a gradation exactly according to the gravure data. If this happens, the cylinder which is halfway engraved is conventionally scrapped, so that it is necessary to perform an engraving operation on a new cylinder from the beginning after power is recovered.
Meanwhile, manufacturing of a plate for a gravure takes an enormously long time, and a cylinder which is used as a plate material is expensive. Hence, even if power failure occurs, it is desirable not to waste engraving heretofore completed and to effectively use a cylinder which is halfway engraved. To this end, a plate manufacturing apparatus with an uninterruptive power supply attached thereto may be used. Such a photogravure plate manufacturing apparatus successively performs engraving, using a back-up power source which is installed within an uninterruptive power supply, even if power failure occurs, so that engraving on one cylinder is completed without an interruption. However, since engraving takes an enormously long time (30 minutes to 1 hour, for example, to engrave one cylinder), to complete engraving on one cylinder without any interruption, the back-up power source of the uninterruptive power supply must have a large capacity. Further, even if the back-up power source has a large capacity, if an interval between the current power failure and next power failure after recovery of power is short, since a storage battery which serves as the back-up power source is not charged up sufficiently, interruption of engraving due to the next power failure may be inevitable.